The state of the art is believed to include the following US Patents listed below.
4,688,026August 1987Scribner et al.6,378,276April 2002Dorge et al.6,248,963June, 2001Gottlober6,817,522November 2004Brignone, et al.6,712,276March 2004Alabi et al.6,693,539February 2004Bowers, et al.6,377,058 B1June, 2002Pemrick